Penicillic acid-mediated quorum-sensing inhibition suppresses motility and virulence of Xanthomonas albilineans

Sugarcane leaf scald, caused by Xanthomonas albilineans , is a significant bacterial disease that poses a substantial threat to global sugar production. The quorum-sensing (QS) system in X. albilineans presents a promising target for anti-virulence strategies. Here, we demonstrate that penicillic acid exhibits potent antibacterial activity against X. albilineans , with a minimum inhibitory concentration (MIC) of 6 μg/mL and an effective concentration for 50 % inhibition (EC₅₀) of 3.703 μg/mL. Transcriptome analysis, molecular docking, and surface plasmon resonance (SPR) confirmed that penicillic acid competitively binds the sensory histidine kinase RpfC, disrupting DSF-mediated QS signaling. At sub-inhibitory concentrations (½ MIC), penicillic acid significantly suppressed twitching, swimming, and swarming motility by downregulating genes associated with type IV pili, flagellar assembly, and chemotaxis. At full MIC, direct binding of penicillic acid to the FlgE and CheW proteins further impaired motility. These findings elucidate the molecular mechanism of penicillic acid and support its potential as a quorum-sensing inhibitor for biocontrol of sugarcane leaf scald.